Record disk for talking machines and the like



Patented Feb. 19, 1929.

' UNITED S TATE S PATENT OFFICE.

WILLIAM EORSE, OF LONDON, ENGLAND, ASSIGNOB TO COLUMBIA PHONOGRAPH CQM.TPANY, INC., 01 BRIDGEPORT, CONNECTICUT, A CORPORATION OF NEW YORK.

RECORD DISK FOR TALKING MACHINES AND THE LIKE.

No Drawing.

conditions, and be free from the difficulties;

that have been associated with records produced from the usual shellacmixtures.

The invention relates more especially to record disks having an innercore or disk made of a cheaper material than is used for the surface onwhich the record sound groove is impressed.

Disks of this class are constructed in many different ways, some havinga cardboard disk prepared with a suitable filler or gum, and then coatedon the surface with a high-grade mixture comprising shellac, pigment,flock, or shoddy, together with certain mineral earths and clays.

Another well-known method for making records of this class is bypulverizing a shellac mixture similar to the above, and then dusting,the powder by means of a sieve onto one surface of thin paper diskswhich have been out about the size of a finished record and treated witha suitable gum to hold the shellac powder when so duste A sheet preparedin the above manner is placed with the shellac face downwards on thematrix plate in the record forming die, a disk or piece of cheapermaterial (such as powdered earths, clays and shoddy, bound together witha suitable gum so as to form a thermoplastic mass) is softened by heatand placed on the back of the shellac coated paper sheet. The other halfof the record forming die-isthen placed in position, and the whole Ysubjected to hydraulic or other pressure so as to impress the shellacsurface of the coated paper sheet with the sound record line on thematrix, the cheaper material beingextended out to form the inner body ofa record disk of suitable thickness and strength for comniercial use.Laminated-records having a shellac mixture surface as described above,invariably have a'serious fault in that the record surface is notstable. Particles of mineral or flock that are too large to com ressbetween the very fine consecutive recor grooves and that rocess ofApplication filed October 17, 1924. Serial No. 744,257.

cannot be properly worked up on the record surface owing to theinefficient mixing, alter in shape by shrinkage or expansion and whenexposed to the heat or damp as certain partic es that are notsutficiently covered with shellac get loose or form slight projectionsor recesses, thus producing a miscroscopically rough surface which,while being passed over by a reproducer stylus, produces undesirablescratching noises.

In the manufacture of records in the past this fault has arisen from theuse offlock or other fibrous material in combination with the shellacand other ingredients for the pur-. pose of binding the small particlestogether as the particles of mineral earths and the like were not groundfine enough to give suflicient granular surface to enable such to bebound efi'ectively by the shellac. This difiiculty has even arisen ifonly a very small proportion of the unbound material exists, as suchwill invariably work up on the surface of the recordand break away orgive roughness.

This serious fault has not, up to the present, been successfullyovercome, owing to the difficulty in preparing a sufficiently fine andpowdered record material that is entirely free from large grains ofmineral or other material, as grains having a diameter of about -180 mm.would be likely to work loose when in use. The present inventioninconnection with the manufacture of records provides for the productionof grains having a maximum size of .1 mm. and of averaging about .025mm. in diameter. By this means, the necessity of using flock, or otherfibrous binding material is eliminated, as the granular surface issuflicient to be tightly bound by shellac alone, while the particles ofmineral earths and the like are all so small that they do not present asurface rough enough to cause the stylus to vibrate to any audible note.

When manufacturing the improved records, there is employed paper sheetsthat are coated with powder having a maximum granular size of less than.1 mm. and free from any fibrous materials, and the disks or sheets Thisbacking material may contain flock or other binding material, but thisbacking or strengthening material forms no part of produced by mixingthematerials, for instance, mineral earths, resins and coloring matter, intheir correct proportlons and in the usual way by first heating androlling the product out into slabs, and then grinding such slabs to afine powder by passing them through impact mills, rolling mills or thelike. Having thus secured a fine powder, it is passed into a separatingbox to enable the fine granules to be separated from the coarsergranules by air flotation.

The separation is effected by air flotation by passing the powder directfrom the grind-' ing mills into a separating box at a point about halfway up its height, and there is mounteda suction fan or exhauster on thetop of the separating box above the powder inlet. By the operation ofthis fan or exhausting device there is created a partial vacuum whichcauses the air to be removed from the separating box at a high velocity.This air displacement, when used in conjunction with apparatus ofsuitable size, will create a current of air having the necessary forceto carry away all particles of powder entering the chamber which areunder a given size (.1 mm. in diameter for example), while the heavierparticles fall to the bottom of the chamber to be returned by conveyormeans back to the grinding mills, where it is reground and repassedthrough the separating chamber again and again until it is of sufficientsize to pass over with the air current into a receptacle adapted tocollect the very fine powder which is required for the invention.

It must be understood that the action and construction of 'the powderseparating mechanism is described by way of example only, and may bevaried in many ways, or a sieve of suitably fine mesh or anyotherwell-known means for obtaining fine powder of a defined .maximumsize may be used.

' The finely divided powdered shellac material thus obtained is dustedby any well known mechanical means on to disks of paper of suitable sizefor forming records. The coated paper sheets, while warm, may then bepassed between cold (preferably watercooledi rollers under pressure togive an even surface to the powder, and to distribute the powder evenlyover the paper disk.

This improved cold rolling process has not hitherto been practicablewith the coarser grained powder, owing to the large particles becomingdepressed temporarily into the paper sheet and then rising again whenreleased and forming excretions or irregularities that were damaging tothe surface of the powdered sheet.

The thermoplastic powder having the char acteristics as describedherein, may be used for manufacturing sound record disks in variouswell-known ways; and although primarilycintended for use in combinationwith paper disks to limit the use of the high-grade powder in the soundrecords surface, it must be understood that such finely divided andseparated powder as hereinbefore described can also be applied tovarious forms of core or disk without necessarily using paper sheets.

It is to be understood that the foregoing description given for securinga complete adhesion of the finely divided homogeneous material withoutthe necessity of using a foreign binding material, such as flock, is setforth by way of example or illustration, and

not of limitation, and that the powder may be composed of variousingredients and produced in various ways to suit t-heparticular purposefor which it is required.

Having now particularly described and ascertained the nature of theinvention, and in what manner the same is to be performed, what isclaimed is:

1. A. sound record comprising a base of material containing a fibrousbinder, the layer of said base into which the record groove is pressedbeing of smoother texture than the material of the base said layercomprising shellac and a granular filler free of fibrous binders thegranules having a size not exceeding one-tenth mm. indiameter.

2. A. sound record having an outer layer into which the record groove ispressed, said layerv consisting of a compressed dried mechanical mixtureof granules composed of sirellac and crocus having a size not exceedingmm.

3. A sound record having a base with fibers therein and an outer layerinto which the record groove is pressed, said layer consisting of acompressed granular mixture of shellac and filler, said mixture beingfree of fibrous binding materials, and the granules of said mixturehaving a size not exceeding .1 mm;

Signed at London, England, this sixth day of Uctober A. D. 1924.

. 7 WILLIAM FORSE.

